We were contracted by Areus Engineering to develop a control system for a passive LED matrix of up to 768 white LEDs (48x16 pixels). The LED-matrix was attached to a scale model of the prototype for a Maybach car. The idea of Michal Plata was to make the car sort of invisible by recording video from one side with a webcam and projecting it to the other side. (If you've seen the James Bond movie "Die Another Day", you'll know what I mean ;) ). "sort of invisible" because of course with blocky 48x16 pixels and no colors you could never do an accurate representation....

The LED control-system should be able to receive pixeldata from an attached PC and do 16 shades of gray. With this configuration our system managed to display 15fps with a refresh rate of up to 100Hz. The pixeldata came from a webcam attached to a Linux Netbook. On this computer the image was scaled an dedistorted using OpenCV and transferred to the LED-screen using ledbridge.

The controller had to drive the 15mA rated LEDs at 240mA to achieve the full brightness while scanning through the 16 rows, yet never stop scanning the matrix because that would burn out the LEDs instantly! Achieving the high frame- and refresh-rate with the ATMega32 was a difficult task, I had to think of an optimized framebuffer layout to decode the incoming pixeldata to in order to achieve the high refresh rate. Also I had to use assembler because with C the required performance just can't be reached.

Video ´the invisible Maybach´ by Michal Plata, 2010